This invention relates to an electronic breaker trip device for controlling the tripping of a circuit breaker, and more particularly relates to a novel solid state circuit arrangement for an electronic trip device.
Electronic trip devices are generally well known and are shown, for example, in U.S. Pat. Nos. 3,766,436; 3,792,313; 3,801,872; 3,914,667 and 3,970,899, all assigned to the assignee of this application.
In arrangements of the prior art, a relatively high power supply current is required by the circuitry. To overcome this requirement, relatively complicated approaches have been taken to establish the power supply. In a first approach, for example, two controlled rectifiers are connected in series with the primary of each intermediate current transformer which monitors the circuit breaker current. A zener diode is then placed in series with each controlled rectifier gate. Each alternate cycle of the signal current then generates a high voltage across each controlled rectifier for a short portion of the cycle to prevent transformer saturation and damage. This high voltage is then bled off to establish the power supply.
The major disadvantage of this approach is that many electronic components are needed to establish the power supply (including, for example, six controlled rectifiers and six zener diodes for a three-phase system) and this large component count decreases reliability and increases cost.
A second approach which has been taken is to provide a separate set of primary current sensors to generate the power for the circuit. In addition to the added cost of the extra sensors, the power supply now becomes sensitive to transients produced in the primary current.